The subject matter of the present invention is a method for the cleavage of organosiloxanes by means of hydrogen chloride, resulting in the formation of organochlorosilanes, which are important starting products for the preparation of protective-group reagents used, for example, in the production of synthetic penicillins. Furthermore, the organochlorosilanes are foreproducts for the broad fields of application of the organosilicon esters and silicones.
Organosiloxanes are often produced in contaminated form in many fields of activity. For example, hexamethyldisiloxane forms as a waste product in protective-group chemistry, or it is contained in addition to other siloxanes in used silicone oils which have served, for example, as heat carriers or hydraulic oils. There has formerly been virtually no use for these used silicone oils, so that they have had to be rendered harmless or destroyed in large quantities.
Several attempts have already been made to render the valuable organosiloxane wastes reusable by cleaving the siloxanes to chlorosilanes. On the other hand, the methylchlorosilanes, for example, have been available on a large technical scale only through Rochow synthesis, and therefore their supply is dependent upon this method of synthesis. Thionyl chloride, aluminum chloride and phosphorus trichloride have already been described as cleavage reagents. A disadvantage in the use of these compounds is the high percentage of byproducts which are produced, and whose separation entails additional expense.
It is furthermore also known to cleave siloxanes by means of hydrogen chloride. These attempts, however, were performed in the presence of water-binding additives, such as concentrated sulfuric acid or ZnCl.sub.2 in order to influence the otherwise incomplete reaction. Here, again, undesired byproducts are formed.
In German Offenlegungsschrift No. 3,013,920 a method is described for performing the cleavage with hydrogen chloride at an excess hydrogen chloride pressure in order to arrive at a complete transformation to chlorosilanes, which otherwise cannot be achieved at room temperature. According to the procedure therein described, a high yield of the desired chlorosilanes is achieved, but this process has the disadvantage of the high technical complexity that is involved in working with hydrogen chloride under pressure.
The problem therefore existed of performing the cleavage of organichlorosilanes with hydrogen chloride such that the desired organochlorosilane will be produced directly in high yields by this reaction, and the investment in apparatus will be as low as possible.